1. Field of the Invention
This invention relates to photogrammetric imaging systems and, in particular to a dual-swath electro-optical imaging system for use in fixed wing aircrafts, helicopters, and unmanned aerial vehicles (UAV) to acquire large-format, wide-swathwidth color imagery with centimeter-level resolution.
2. Description of Related Art
Remote sensing applications from natural disaster response to warfighting and peace keeping operations require an advanced airborne imaging system to provide fast and large format geo-referenced and orthorectified image maps.
Many airborne digital frame camera systems have come into use for mapping, reconnaissance, and surveillance applications. A major limitation is the size of the CCD and CMOS area arrays currently available for use in such systems. As a result, widespread use of digital aerial photographic systems has occurred featuring multiple arrays, multiple lenses or multiple cameras in order to provide large ground coverage and big image format at a high ground resolution by a single flight.
In an article by Gordon Petrie entitled “Systematic Oblique Aerial Photography Using Multiple Digital Frame Cameras”, published February 2009 in Photogrammetric Engineering and Remote Sensing, various twin cameras systems, and multiple camera systems are described. Twin camera systems include “DiMAC” Wide from DiMAC Systems in Belgium, a Dual-DigiCAM system from IGI in Germany and a Rollei Metric (now Trimble) in Germany. All three of these twin camera units have a rather similar specification with each individual camera module having a digital image sensor back that produces images of 7.2K×5.4K=39 megapixels in size. Their camera shutters are synchronized to operate simultaneously to obtain two oblique photos on either side of the flight line. After the rectification and the stitching together of the two rectified images, the final merged (near-vertical image is 10.5K×7.2K=75 megapixels in size. However, the tilted photographs acquired by oblique cameras have fan shaped imaging areas with variable resolutions across the different parts of the images. Those tilted photographs need extra work to be converted into the rectified images for Geographic Information System (GIS) application needs. Extra cost is associated with these extra tilted-photograph processes, including to correct the fan shaped images with variable resolution to rectangular images with data interpolation, which wastes the precious image resources, introduces artifices, and sacrifices image quality.
U.S. Pat. No. 7,009,638 issued Mar. 2, 2006 to Michael Gruber et al. and assigned to Vexcel Imaging GmbH, discloses a large format digital camera system exposing multiple detector arrays with one or more single lens systems to acquire sub-images of overlapping sub-area of large area objects. The sub-images are stitched together to form a large format, digital macroimage which can be colored. However, this camera system typically uses four (4) lenses and fifteen (15) 35 mm format area sensor arrays, and is a fairly complicated system. The hardware is massive and heavy. It is complicated to build, calibrate, operate, and maintain. With 15 critical non-redundant sub-systems, it means a higher failure rate. Its lens set is fixed and unlikely to have an interchangeable option. Its composite image is asymmetrically overlapped and stitched. The patented processing solutions suggested many compromised options which means problematical. This system is unlikely to be widely accepted by the aerial photogrammetric and GIS industry even though the system manufacture has been sold to a large software manufacturer.